1. Field of the Invention
The present invention relates to a method of fabricating a semiconductor device.
2. Description of the Related Art
FIGS. 7A through 7H are cross-sectional views illustrating the fabricating processes until a wafer, at which are formed a plurality of semiconductor elements forming a widely used semiconductor, is separated into the respective semiconductor elements. These steps are as follows.
In FIG. 7A, a wafer 1 formed by a plurality of semiconductor elements is readied. Generally, the material of the wafer 1 is silicon.
As shown in FIG. 7B, in order to cut the reverse surface of the wafer 1 to a desired thickness, a protective tape 2 for back grinding is adhered to the front surface (i.e., the surface at which the semiconductor elements are formed) of the wafer 1.
The protective tape 2 for back grinding is formed by a tape substrate 21 and an adhesive 22. In consideration of the method for conveying the wafer 1, the material and the thickness of the tape substrate 21 are such that the wafer 1 does not bend. A tacky resin, a UV-curing resin or the like is used for the adhesive 22.
As shown in FIG. 7C, the wafer 1 is cut (subjected to back grinding processing) to a desired thickness by an unillustrated cutting device (back grinder). As shown in FIG. 7D, the protective tape 2 for back grinding is peeled off. When the adhesive 22 of the protective tape for back grinding is a tacky resin, the protective tape 2 is peeled off mechanically. When the adhesive 22 of the protective tape for back grinding is a UV-curing resin, the protective tape 2 is peeled off after being irradiated by UV light such that the adhesiveness of the protective tape 2 is deteriorated. Thereafter, the wafer 1 may be washed.
Next, in FIG. 7E, by using a probe needle 7 or the like, it is determined whether the wafer 1 has the desired electric characteristics. Namely, the wafers 1 are inspected (probed) and the good and bad wafers are discriminated by ink marking, mapping or the like.
Thereafter, in order to divide (dice) the wafer 1 into the separate semiconductor elements formed thereon, as illustrated in FIG. 7F, a protective tape 3 for dicing is adhered to the reverse surface of the wafer 1.
The protective tape 3 for dicing is formed by a tape substrate 31 and an adhesive 32. UV-curing resin is widely used for the adhesive 32.
In FIG. 7G, cutting grooves 4, which are of a thickness such that they extend through the entire thickness of the wafer 1 and about one-half of the thickness of the protective tape 3 for dicing, are formed by a dicing device (not shown) such that the wafer 1 is divided into sizes of the respective semiconductor elements.
Then, the entire surface of the protective tape 3 for dicing is irradiated with UV light such that the adhesiveness of the protective tape 3 for dicing is deteriorated. Thereafter, as illustrated in FIG. 7H, separate semiconductor elements 11 and protective tape 3 for dicing are picked up with a pick up tool 5 of a dice bonding device, and the semiconductor elements 11 and the protective tape 3 for dicing are separated.
Thereafter, the dice bonding process is carried out, the assembly process is carried out, and packaging is thus completed. The dice bonding process and processes thereafter are well-known, and thus, description thereof will be omitted.
However, there are the following problems with the semiconductor device fabricated by this conventional method.
First of all, as background explanation, the size of wafers has gradually increased from 6 inch (about 150 mm) wafers and 8 inch (about 200 mm) wafers to 12 inch (about 300 mm) wafers, and accordingly, the thickness thereof has also become more thick. (6 inch wafers have a thickness of about 625 xcexcm, whereas 8 inch wafers have a thickness of about 725 xcexcm.)
However, because the wafer thickness (more correctly, chip thickness) is limited due to the package on which the semiconductor elements are placed, in order to not change the chip thickness, the amount of the wafer which is to be cut increases, and the mechanical strength of the wafer deteriorates.
Further, in recent years, the demand for thinner packages has increased, and in order to handle such a demand, wafers have had to be made thinner. For example, in order to place semiconductor elements on a thin package such as an IC card, the upper limit of the wafer thickness is about 150 xcexcm.
In light of the above-described background, the following problems arise when the wafer is made thin (particularly to a level of 150 xcexcm).
(1) When the protective tape for back grinding is peeled off after the back grinding processing of the wafer is completed, the wafer may break. Defects arise which ultimately result in an increase in costs.
(2) During probing which is carried out after the protective tape for back grinding has been peeled off, due to the pressure applied to the wafer by the probing needle, the wafer may break. Defects arise which ultimately result in an increase in costs.
(3) When the protective tape for dicing is adhered after probing, the wafer may break. Defects arise which ultimately result in an increase in costs.
(4) While the wafer is being conveyed during the above-described processes, due to the wafer bending or the like, the wafer may break. Defects arise which ultimately result in an increase in costs.
(5) As a countermeasure to such problems, the wafer (chip) has been made thick. Thus, it is difficult to apply such wafers to thin packages, and the other materials (particularly the package material covering the chip) have been made thinner, resulting in deterioration in quality such as a deterioration in moisture-resistance, soldering-resistance and the like.
In order to overcome the above-described problems, in accordance with the method of fabricating a semiconductor device of the present invention, after the protective tape for back grinding is adhered to the front surface of the wafer and back grinding processing is carried out, with the protective tape for back grinding still adhered, the tape-shaped adhesive for dice bonding is adhered to the reverse surface of the wafer which has been subjected to the back grinding processing, and through a dicing process or the like, dice bonding is carried out by using the tape-shaped adhesive for dice bonding.
In accordance with the present invention, the tape-shaped adhesive for dice bonding is adhered to the wafer which has been subjected to back grinding processing. Thus, the wafer can be prevented from breaking, the yield can be improved, and costs can be reduced. The wafer can be made thin and use of a thin package becomes possible, without the quality deteriorating. Further, a process for applying an adhesive at the time of dice bonding can be omitted.